1. Field of the Invention
The present invention relates to divided blade and slit-forming blade constituting the front and rear curtains of a focal plane shutter of the camera positioned near the exposure aperture of a camera and disposed between the lens and the film in the camera.
2. Related Background Art
Conventional TTL light adjustment has encountered exposure results of photographing that are widely dispersed depending on conditions of a subject since such conventional TTL light adjustment is performed in a manner that the quantity of flashing light is controlled so that the average value, across a specific area of film surface, of exposure light reflected from a subject and incident on the film surface and adapted to be received by a photoreceptor device for monitoring, reaches a predetermined exposure light level when flashing light is adjusted.
For example, in the case of a camera having a photoreceptor device enabled to receive light incident to the entire exposure area of the film surface, if a photograph is taken using light flashing in a field where a main subject occupies a small area and the background of the main subject constitutes a wide space, the portion that does not reflect the flashing light becomes wide, and thereby, the quantity of reflected light received by the photoreceptor is smaller, so that the quantity of flashing light so controlled becomes greater and may cause over-exposure for the main subject.
On the other hand, if a photograph is taken using light flashing in a field where an object of a high rate of reflection such as a gold-leafed folding screen is standing right behind a main subject in the case of the same cameras as above, the quantity of reflected light received by the photoreceptor is greater, so that, as a result, the quantity of flashing light so controlled becomes greater and may cause under-exposure for the main subject.
To solve this problem, a TTL automatic light adjustment control device has been proposed in a Japanese Patent Laid-open Publication 3-68928 as means for eliminating dispersion in the light exposure for a main subject due to difference between conditions of factors for subjects in the subject field such as the location and rate of reflection for such subjects in photographing using light flashing.
The TTL automatic light adjustment control device, or simply, the automatic control device, has a plurality of photoelectric means disposed at positions where the photoelectric means can receive light reflected by the film surface, the plurality of photoelectric means each being capable of measuring the light reflection intensity from each of regions of subject field obtained by dividing the subject field into one single central region and a plurality of peripheral regions.
In the process, preliminary flashing of a flashing device is activated immediately before the focal plane shutter of a camera is opened so that the preliminary flashing light is firstly reflected by the subjects onto the lens-side surface of the shutter curtain of the focal plane shutter through the lens. The first reflected preliminary flashing light is secondly reflected by the lens-side surface of the shutter curtain of the focal plane shutter, then received and processed by the plurality of photoelectric means corresponding to the respective regions of the subject field.
The automatic control device integrates the light reflection intensity values outputted from each of the plurality of photoelectric means, and outputs these integrations as the detected values for the subject field rates of reflection based on the preliminary flashing light for the respective regions of the subject field.
Thus, the degree of weighting, or the weighting coefficient for each divided region of the subject field is determined such that the determined weighting coefficients enable an optimal exposure to be obtained for the main subject, by integrating computing the detected information on the rates of reflection for the respective regions of the subject field.
Successively, main flashing of the flashing device is activated immediately after the focal plane shutter of the camera is opened so that the reflected main flashing light is received and processed by the same plurality of photoelectric means as described above.
The automatic control device weights the light reflection intensity values of the main flashing that is outputted from the plurality of photoelectric means, with the weighting coefficient predetermined as described above.
The automatic control device then sums up and integrates the weighted outputs, and compares the integrated values of the weighted outputs with predetermined values. Thus, the automatic control device ceases the main flashing according to timing determined by such comparison, thereby completing the light adjustment of the main flashing. Such system of light adjustment is referred to as the "TTL multi-pattern light adjustment".
When a conventional focal plane shutter is used with a TTL automatic light adjustment control device described above, reflected light from the lens-side surface of the shutter curtain is required to reach the photoelectric means described above. Because of this, the lens-side surface of the shutter curtain is processed with high reflection rate painting (hereinafter also referred to as "whitening painting") for increasing the rate of reflection of the surface to a high value substantially equal to that of the film surface. It is noted that the surface of the shutter curtain so painted with a high reflection rate painting may have some variation in the rate of reflection thereof, in which the painted surface may look white to the naked eye when a relatively high reflection rate painting is applied to it, and rather gray to the naked eye when a relatively low reflection rate painting is applied to it. Colors resulting from high reflection rate surfacing painting as described above, including the gray-looking color, may be hereunder referred to as "white", whereby "whitening painting" may be referred to as "graying painting".
Recently, there has been a demand for higher shutter speeds and higher flash synchro speeds due to increased film sensitivity and desire for new image expression, whereby cameras have been provided that implemented a high shutter speed as high as 1/8000 sec. and a flash synchro speed of 1/250 sec.
In focal plane shutters for implementing such high speed photographing, front and rear curtains constituting a shutter curtain of the shutter are each divided into one slit-forming blade and a plurality of (usually around three) divided shielding blades. When a high shutter speed beyond a flash synchro speed is directed, the rear curtain is started moving with a specified temporal gap in the starting time behind the front curtain, and the width of spatial gap, or slit, between the slit-forming blades of the front and rear curtains, is either fixed to a predetermined value or varied in accordance with the speed, thereby enabling the film to be exposed with light through the slit. This exposure method is referred to as "slit exposure".
In the conventional focal plane shutter described above, with slit-side edge surfaces of the shutter curtains thereof covered with whitening painting of high rate of reflection painting that is applied to the shutter curtains, undesirable unevenness of exposure adversely occurs during the slit exposure due to reflection on such slit-side edge surface of the shutter curtains.